LED screens are generally backlit with the aid of LEDs. For this purpose, a plurality of LED modules are interconnected and operated. In this case, the LED modules are connected in series. Each module generally has one blue, one red and one or two green LEDs. These series are then arranged in parallel fashion again in order to achieve a uniform illumination of the screen.
The luminous efficiency of LEDs and in particular of high-power LEDs changes with the lifetime and depending on the temperature. This results in a continual change in the emission spectrum or the color locus (main emission line) on a wavelength or frequency scale. This change is undesirable in principle and results, if the LEDs are used for backlighting LCD screens, in incorrect color representation of still and moving images. These color disturbances can occur both areally and in punctiform fashion.
Hitherto, backlights for screens have been readjusted in their entirety or line by line with regard to their color and their white point. The final setting and calibration are effected after the preassembly of the backlight units (BLU) in the factory. If appropriate, the color is automatically tracked during operation by precisely the entire screen or the individual lines being tracked. However, this does not always lead to high-quality results.